Hitherto, graphite has been used conventionally as a cathode for electrolyzing acid electrolytes containing hydrochloric acid, sulfuric acid, nitric acid, an organic acid or a mixed acid thereof. Graphite is inexpensive and has excellent corrosion resistance and excellent resistance to hydrogen embrittlement. However, graphite has the disadvantage that it has not only a high electric potential for hydrogen generation and a comparatively low electric conductivity but also poor mechanical strength and processing properties. East German Pat. No. 62308 describes reducing the electrolysis voltage by using a cathode having a low hydrogen overvoltage which is prepared by coating graphite with tungsten carbide or titanium carbide by plasma spray coating. However, it is not possible to remove the disadvantages of graphite where it is used as a cathode substrate.
On the other hand, various kinds of cathodes wherein a substrate composed of a metal is coated with a material having a low hydrogen overvoltage are known. For example, a cathode for chlorine-alkali electrolysis wherein a substrate of iron metal is coated with a powdery metal having a low hydrogen overvoltage by flame spray coating is described in Japanese Patent Application (OPI) No. 32832/77. In this cathode, although mechanical strength and processing properties are improved because the substrate is made of metal, there are problems that resistance to corrosion is not sufficient for practical use where the cathode is used for electrolyzing the above-described acid solutions and because the catholyte is an alkaline solution for chlorine-alkali electrolysis.